As computers are spread, inkjet printers have been recently widely used for printing on, for example, paper, film, or fabric at home besides offices.
An inkjet recording method may be a manner of discharging liquid drops by applying pressure by a piezo element, a manner of discharging liquid drops by generating bubbles in an ink by heat, a manner using an ultrasonic wave, or a manner of absorptively discharging liquid drops by an electrostatic force. As an ink for inkjet recording, an aqueous ink, an oily ink, or a solid (melt type) ink is used. Among these inks, the aqueous ink is mainly used from the viewpoints of production, handling property, odor, safety, and the like.
A colorant used in the ink for the inkjet recording needs to ensure high solubility to a solvent, recording at a high concentration, favorable colors, excellent fastness to light, heat, air, water, or chemicals, good settlement to an image-receiving material, low spreading, excellent preservation as an ink, non-toxicity, high purity, and availableness at low price. However, it is very difficult to find a colorant satisfying the requirements at a high level.
In order to improve image preservation properties, particularly light fastness of an image, many suggestions have been conventionally made. For example, Patent Document 1 describes a coloring material (colorant) that may improve light fastness of an image and at the same time form an image with excellent color strength, especially, in a yellow ink having low light fastness of an image, among cyan, magenta and yellow inks. Also, Patent Document 2 describe a method of using an ink including a first coloring material with excellent image fastness, combined with a second coloring material having a different structure from the first coloring material so as to improve light fastness of an image, and form an image excellent in hue, and at the same time to suppress clogging of an ink supply path or improve storage stability.